Imaging lens

ABSTRACT

An imaging lens includes a first lens group and a second lens group, arranged from an object side to an image plane side. The first lens group includes a first lens, a second lens, and a third lens. The second lens group includes a front side lens group and a rear side lens group. The front side lens group includes a fourth lens and a fifth lens. The rear side lens group includes a sixth lens and a seventh lens both having two aspheric surfaces. The imaging lens has a total of seven single lenses. The first to seventh lenses are arranged respectively with a space in between. The third lens has convex surfaces on both sides. The fourth lens has a concave surface on the object side. The fifth lens has a concave surface on the image plane side. The rear side lens group has a specific focal length.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of a prior application Ser. No.15/685,799, filed on Aug. 24, 2017, allowed, which is a continuationapplication of a prior application Ser. No. 15/235,280, filed on Aug.12, 2016 and issued as U.S. Pat. No. 9,772,475 on Sep. 26, 2017, whichclaims priority of Japanese Patent Application No. 2015-171027, filed onAug. 31, 2015.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to an imaging lens for forming an image ofan object on an imaging element such as a CCD sensor and a CMOS sensor.In particular, the present invention relates to an imaging lens suitablefor mounting in a relatively small camera such as a camera to be builtin a cellular phone, a portable information terminal, or the like, adigital still camera, a security camera, a vehicle onboard camera, and anetwork camera.

In these years, in place of cellular phones that are intended mainly formaking phone calls, so-called “smartphones”, i.e., multifunctionalcellular phones which can run various application software as well as avoice call function, have been more widely used. When applicationsoftware is run on smartphones, it is possible to perform functions suchas those of digital still cameras and car navigation systems on thesmartphones. In order to perform those various functions, most models ofsmartphones include cameras.

Generally speaking, product groups of such smartphones are oftencomposed according to specifications for beginners to advanced users.Among them, an imaging lens to be mounted in a product designed for theadvanced users is required to have a high-resolution lens configurationso as to be also applicable to a high pixel count imaging element ofthese years, as well as a small size.

As a method of attaining the high-resolution imaging lens, there hasbeen a method of increasing the number of lenses that compose theimaging lens. However, the increase of the number of lenses easilycauses an increase in the size of the imaging lens. Accordingly, indevelopment of the imaging lens, it has been necessary to achieve highresolution while shortening a total track length (TTL) by restrainingthe increase of the number of lenses or by other method.

In these days, with significant advancement in achieving the higherpixel count of an imaging element and image processing technology, animaging lens has been developed so as to attain higher resolution ratherthan a shorter total track length of the imaging lens. For example,there is a camera unit, which is configured separately from asmartphone, and is composed of a high-resolution imaging lens, animaging element, etc. By attaching the camera unit onto a smartphone, itis achievable to obtain images having equivalent quality to those ofhigh-end model digital still cameras. However, because of the presenceof the camera unit, portability of the smartphone is ruined. Therefore,a smartphone with a built-in camera is superior to such smartphone withan attached camera unit in its convenience and portability. Accordingly,there remains a demand for a small-sized high resolution imaging lens.

In case of a lens configuration composed of seven lenses, due to thelarge number of lenses of the imaging lens, it has high flexibility indesign. In addition, it is achievable to attain satisfactory correctionof aberrations, which are necessary for high-resolution imaging lenses,and downsizing of the imaging lens in a balanced manner. For example, asthe conventional imaging lens having the seven-lens configuration, animaging lens described in Patent Reference has been known.

Patent Reference: Japanese Patent Application Publication No.2012-155223

The conventional imaging lens described in Patent Reference includes afirst lens that has a shape of a biconvex shape, a second lens that hasa shape of a biconcave shape joined to the first lens, a third lens thatis negative and has a shape of a meniscus lens directing a convexsurface thereof to the object side, a fourth lens that is positive andhas a shape of a meniscus lens directing a concave surface thereof tothe object side, a fifth lens that is negative and directs a convexsurface thereof to the object side, a sixth lens that has a biconvexshape, and a seventh lens that has a biconcave shape, arranged in theorder from the object side. According to the conventional imaging lensof Patent Reference, the first through the fourth lenses compose a firstlens group, and the fifth through the seventh lenses compose the secondlens group. With the configuration, by restraining the ratio of a focallength of the first lens group to that of the second lens group within acertain range, it is achievable to downsize of the imaging lens andsatisfactorily correct aberrations.

In case of the conventional imaging lens of Patent Reference, althoughthe size of the imaging lens is small, correction of the image plane isinsufficient and the distortion is especially large. Therefore, there isa limit by itself to achieve high performance imaging lens. With thelens configuration of the imaging lens of Patent Reference, it isdifficult to achieve satisfactory aberration correction while downsizingof the imaging lens.

Here, such a problem is not specific to the imaging lens to be mountedin cellular phones and smartphones. Rather, it is a common problem foran imaging lens to be mounted in a relatively small camera such asdigital still cameras, portable information terminals, security cameras,vehicle onboard cameras, and network cameras.

In view of the above-described problems in conventional techniques, anobject of the present invention is to provide an imaging lens that canattain both downsizing thereof and satisfactory aberration correction.

Further objects and advantages of the present invention will be apparentfrom the following description of the invention.

SUMMARY OF THE INVENTION

In order to attain the objects described above, according to the presentinvention, an imaging lens includes a first lens group having positiverefractive power; and a second lens group having negative refractivepower, arranged in the order from an object side to an image plane side.The first lens group is composed of a first lens, a second lens, and athird lens. The second lens group is composed of a fourth lens, a fifthlens, a sixth lens, and a seventh lens. Here, the term “lens” usedherein refers to an optical element that has refractive power.Therefore, the term “lens” used herein does not include a prism, whichchanges a traveling direction of a light beam, a flat filter, and thelike. Those optical elements may be disposed in front of or behind theimaging lens, or between respective lenses, as necessary.

When the whole lens system has the focal length f and a distance alongthe optical axis from an object-side surface of the first lens to theimage plane is La, the imaging lens of the invention preferablysatisfies the following conditional expression (1):1.2<La/f<1.8  (1)

When the imaging lens satisfies the conditional expression (1), it isachievable to suitably downsize the imaging lens. In these years, thereis an increasing demand for taking images of a wider range through animaging lens. For this reason, there is increasing demand to attain bothdownsizing and a wider angle of view of the imaging lens. Especially incase of an imaging lens to be built in a thin portable device, e.g.smartphones, it is necessary to be able to accommodate an imaging lensin a limited space. Therefore, there is often a strict limitation in alength of the imaging lens in a direction of an optical axis.

According to a first aspect of the invention, when the imaging lens ofthe invention has a maximum image height Hmax, the imaging lenspreferably satisfies the following conditional expression (2):1.3<La/Hmax<1.8  (2)

In case of the imaging lens of the invention, it is preferred to haveair (gaps filled with air) between the respective lenses, the first lensthrough the seventh lens, arranged as described above. With those gapsbetween the lenses arranged as described above, the imaging lens of theinvention will not include any cemented lens. In such a lensconfiguration, it is possible to form all the seven lenses that composethe imaging lens from a plastic material. Therefore, it is achievable tosuitably restrain the manufacturing cost of the imaging lens.

In case of the imaging lens of the invention, each of the first throughthe seventh lenses is preferably formed to have an aspheric shape onboth surfaces thereof. Forming both surfaces of each of the lenses asthe aspheric shapes, it is achievable to more satisfactorily correctaberrations from proximity of the optical axis of the lens to theperiphery thereof. Especially, aberrations at periphery of the lens willbe satisfactorily corrected.

The first lens group preferably includes the first lens having positiverefractive power, the second lens having negative refractive power, andthe third lens.

The second lens group preferably includes a front side lens group havingnegative refractive power and a rear side lens group having positiverefractive power. The front side lens group preferably includes thefourth lens and the fifth lens. The rear side lens group preferablyincludes the sixth lens and the seventh lens.

According to the imaging lens of the invention having theabove-described configuration, the arrangement of the refractive poweris “positive-negative-positive” for the first lens group, the front sidelens group, and the rear side lens group. As a result, it is achievableto satisfactorily correct the aberrations.

According to a second aspect of the invention, when the whole lenssystem has a focal length f and a distance along the optical axisbetween the first lens group and the second lens group is Da, theimaging lens having the above-described configuration preferablysatisfies the following conditional expression (3):0.05<Da/f<0.3  (3)

When the imaging lens satisfies the conditional expression (3), it ispossible to correct a chromatic aberration, astigmatism, a fieldcurvature, and a distortion in a balanced manner, while downsizing theimaging lens. When the value exceeds the upper limit of upper limit of0.3, it is advantageous for downsizing of the imaging lens. However, itis difficult to secure a back focal length. Moreover, the axialchromatic aberration is insufficiently corrected (a focal position at ashort wavelength moves to the object side relative to that at areference wavelength).

In addition, the chromatic aberration of magnification is excessivelycorrected (an image-forming point at a short wavelength moves in adirection to be away from the optical axis relative to that at areference wavelength). Moreover, in the astigmatism, the sagittal imagesurface tilts to the image plane side, so that the astigmatic differenceincreases. Moreover, in the image-forming surface curves towards theimage plane side, and the field curvature is excessively corrected. Inaddition, the distortion increases in the positive direction. Therefore,it is difficult to obtain satisfactory image-forming performance.

On the other hand, when the value is below the lower limit of 0.05, itis easy to correct the chromatic aberration. However, in theastigmatism, the sagittal image surface tilts to the object side, andthe astigmatic difference increases. In addition, an image-formingsurface curves towards the object side and the field curvature isinsufficiently corrected. Therefore, it is difficult to obtainsatisfactory image-forming performance.

According to a third aspect of the invention, when the first lens has anAbbe's number νd1, the second lens has an Abbe's number νd2, and thethird lens has an Abbe's number νd3, the imaging lens preferablysatisfies the following conditional expressions (4) through (6):35<νd1<75  (4)15<νd2<35  (5)35<νd3<75  (6)

When the imaging lens satisfies the conditional expressions (4) through(6), it is achievable to satisfactorily correct the chromatic aberrationin the first lens group.

According to the imaging lens of the invention, the first lens ispreferably formed in a shape so as to direct a convex surface thereof tothe object side, and the seventh lens is preferably formed in a shape soas to have a positive curvature radius on an image plane-side surfacethereof, i.e., so as to be formed in a shape directing a concave surfacethereof to the image plane side near the optical axis.

According to the imaging lens of the invention, it is preferred that thefirst lens has positive refractive power, the second lens has negativerefractive power, the third lens has positive refractive power, and thefourth lens has negative refractive power.

With such refractive power of the first lens to the fourth lens, thearrangement of the refractive power is“positive-negative-positive-negative” from the first lens to the fourthlens from the object side. Such the lens configuration, in whichpositive refractive power and negative refractive power are alternatelyarranged, is very effective configuration to restrain the Petzval sum.With the lens configuration described above, it is achievable tosatisfactorily correct the astigmatism and the field curvature.

According to the imaging lens of the invention, the fourth lens ispreferably formed in a shape so as to have a negative curvature radiuson the object-side surface thereof. Here, such a shape to have thenegative curvature radius on the object-side surface thereof, there aretwo types of shapes, i.e., a shape of a meniscus lens directing aconcave surface thereof to the object side near the optical axis and ashape of a biconcave lens near the optical axis.

According to a fourth aspect of the invention, when the whole lenssystem has the focal length f and a curvature radius of the object-sidesurface of the fourth lens is R4f, the imaging lens of the inventionpreferably satisfies the following conditional expression (7):−0.6<R4f/f−0.1  (7)

According to a fifth aspect of the invention, when the whole lens systemhas the focal length f and a curvature radius of the image plane-sidesurface of the fourth lens is R4r, the imaging lens of the inventionpreferably satisfies the following conditional expression (8):−1.2<R4r/f<−0.3  (8)

According to the imaging lens of the invention, the fourth lens ispreferably formed in a shape so that curvature radii of an object-sidesurface and an image plane-side surface are both negative, i.e., so asto be formed in a shape of a meniscus lens directing a concave surfacethereof to the object side near the optical axis.

When the fourth lens is formed in a shape of a meniscus lens directing aconcave surface thereof to the object side near the optical axis asdescribed above, the imaging lens of the invention preferably furthersatisfies the above conditional expressions (7) and (8).

According to a sixth aspect of the invention, when the whole lens systemhas the focal length f and a curvature radius of the image plane-sidesurface of the seventh lens is R7r, the imaging lens of the inventionpreferably satisfies the following conditional expression (9):0.2<R7r/f<0.6  (9)

According to the invention, it is preferred that the sixth lens haspositive refractive power and the seventh lens has negative refractivepower.

In addition, according to the invention, the sixth lens and the seventhlens are preferably formed as aspheric surfaces having an inflexionpoint on at least one of surfaces of each of those lenses.

According to a seventh aspect of the invention, when the fourth lens hasan Abbe's number νd4, the imaging lens having the above-describedconfiguration preferably satisfies the following conditional expression(10):15<νd4<35  (10)

When the imaging lens satisfies the conditional expression (10), it isachievable to more satisfactorily correct the chromatic aberration.

According to an eighth aspect of the invention, when the whole lenssystem has the focal length f and the first lens group has a focallength F1, the imaging lens having the above-described configurationpreferably satisfies the following conditional expression (11):0.6<F1/f<1.3  (11)

When the imaging lens satisfies the conditional expression (11), it isachievable to satisfactorily restrain the chromatic aberration and theastigmatism within satisfactory ranges, while downsizing the imaginglens. When the value exceeds the upper limit of 1.3, the axial chromaticaberration is excessively corrected (a focal position at a shortwavelength moves to the image plane side relative to that at a referencewavelength).

In addition, the chromatic aberration of magnification is insufficientlycorrected (an image-forming point at a short wavelength moves in adirection to be close to the optical axis relative to that at areference wavelength). In the astigmatism, the sagittal image surfacetilts to the image plane side and the astigmatic difference increases.The field curvature is excessively corrected. For this reason, it isdifficult to obtain satisfactory image-forming performance. On the otherhand, when the value is below the lower limit of 0.6, it is advantageousfor downsizing the imaging lens. However, the axial chromatic aberrationis insufficiently corrected and the chromatic aberration ofmagnification is excessively corrected. Moreover, in the astigmatism,the sagittal image surface tilts to the object side, and the astigmaticdifference increases. Therefore, it is difficult to obtain satisfactoryimage-forming performance.

According to a ninth aspect of the invention, when the first lens grouphas the focal length F1 and the second lens has a focal length f2, theimaging lens having the above-described configuration preferablysatisfies the following conditional expression (12):−8<f2/F1<−1.5  (12)

When the imaging lens satisfies the conditional expression (12), it isachievable to satisfactorily correct the chromatic aberration, theastigmatism, and a coma aberration, while downsizing the imaging lens.When the value exceeds the upper limit of −1.5, the axial chromaticaberration is excessively corrected and the chromatic aberration ofmagnification is insufficiently corrected. In addition, an inner comaaberration increases for off-axis light fluxes. Moreover, in theastigmatism, the sagittal image surface tilts to the image plane side,and the astigmatic difference increases. The field curvature isexcessively corrected. Therefore, it is difficult to obtain satisfactoryimage-forming performance.

On the other hand, when the value is below the lower limit of −8, it isadvantageous for downsizing of the imaging lens. However, the axialchromatic aberration is insufficiently corrected and the astigmaticdifference increases. In addition, an outer coma aberration increasesfor off-axis light fluxes, so that it is difficult to obtainsatisfactory image-forming performance.

According to a tenth aspect of the invention, when the front side lensgroup has a focal length Ff and the rear side lens group has a focallength Fr, the imaging lens having the above-described configurationpreferably satisfies the following conditional expression (13):−1.5<Ff/Fr<−0.1  (13)

When the imaging lens satisfies the conditional expression (13), it isachievable to restrain the chromatic aberration, the astigmatism, andthe distortion within satisfactory ranges in a balanced manner. When thevalue exceeds the upper limit of −0.1, the chromatic aberration ofmagnification is excessively corrected. In addition, in the astigmatism,the sagittal image surface tilts to the object side, and the astigmaticdifference increases.

In addition, the distortion increases in a positive direction.Therefore, it is difficult to obtain satisfactory image-formingperformance. On the other hand, when the value is below the lower limitof −1.5, the axial chromatic aberration and the chromatic aberration ofmagnification are both insufficiently corrected. In addition, theastigmatism, the sagittal image surface tilts to the image plane sideand the astigmatic difference increases. Therefore, it is difficult toobtain satisfactory image-forming performance.

According to an eleventh aspect of the invention, when the whole lenssystem has the focal length f and a distance along the optical axisbetween the front side lens group and the rear side lens group is Db,the imaging lens having the above-described configuration preferablysatisfies the following conditional expression (14):0.02<Db/f<0.1  (14)

When the imaging lens satisfies the conditional expression (14), it isachievable to satisfactorily correct the astigmatism, the distortion,and the field curvature in a balanced manner. When the value exceeds theupper limit of 0.1, the distortion increases in a positive direction. Inaddition, the astigmatic difference increases. Therefore, it isdifficult to obtain satisfactory image-forming performance.

On the other hand, when the value is below the lower limit of 0.02, thedistortion increases in the negative direction. In addition, in theastigmatism, the sagittal image surface tilts to the object side and theastigmatic difference increases. The image-forming surface curves to theobject side, and the field curvature is insufficiently corrected.Therefore, it is difficult to obtain satisfactory image-formingperformance.

According to a twelfth aspect of the invention, when the whole lenssystem has the focal length f and the rear side lens group has the focallength Fr, the imaging lens having the above-described configurationpreferably satisfies the following conditional expression (15):1<Fr/f<10  (15)

When the imaging lens satisfies the conditional expression (15), it isachievable to satisfactorily correct the chromatic aberration, theastigmatism, and the distortion, while downsizing the imaging lens. Inaddition, when the imaging lens satisfies the conditional expression(15), it is also achievable to restrain an incident angle of a lightbeam emitted from the imaging lens to an image plane of an imagingelement within the range of a chief ray angle (CRA). As is well known, aso-called chief ray angle (CRA) is set in advance for an imagingelement, i.e. a range of an incident angle of a light beam that can betaken in the image plane. When a light beam outside the range of CRAenters the imaging element, “shading” occurs, which is an obstacle forachieving satisfactory image-forming performance.

When the value exceeds the upper limit of 10 in the conditionalexpression (15), it is advantageous for downsizing of the imaging lens.However, since the astigmatic difference increases in the off-axis lightfluxes, it is difficult to obtain satisfactory image-formingperformance. On the other hand, when the value is below the lower limitof 1, it is easy to correct the chromatic aberration. However, thedistortion increases in a positive direction and the astigmaticdifference increases. Therefore, it is difficult to obtain satisfactoryimage-forming performance. Moreover, it is difficult to restrain theincident angle of a light beam emitted from the imaging lens within therange of CRA.

According to a thirteenth aspect of the invention, when the whole lenssystem has the focal length f and the fourth lens has a focal length f4,the imaging lens having the above-described configuration preferablysatisfies the following conditional expression (16):−3<f4/f<−1  (16)

When the imaging lens satisfies the conditional expression (16), it isachievable to satisfactorily correct the chromatic aberration, theastigmatism, the field curvature, and the distortion in a balancedmanner. When the value exceeds the upper limit of −1, the axialchromatic aberration is excessively corrected and the chromaticaberration of magnification is insufficiently corrected. Moreover, inthe astigmatism, the sagittal image surface tilts to the object side,and the astigmatic difference increases. The field curvature isinsufficiently corrected. Therefore, it is difficult to obtainsatisfactory image-forming performance.

On the other hand, when the value is below the lower limit of −3, theaxial chromatic aberration and the chromatic aberration of magnificationare both insufficiently corrected. In addition, in the astigmatism, thesagittal image surface tilts to the image plane side and the astigmaticdifference increases. In addition, the field curvature is excessivelycorrected, and the distortion increases in the positive direction.Therefore, it is difficult to obtain satisfactory image-formingperformance.

According to the imaging lens of the invention, the fifth lens ispreferably the lens having the weakest refractive power in the secondlens group.

Moreover, according to a fourteenth aspect of the invention, when thewhole lens system has the focal length f and the fifth lens has a focallength f5, the imaging lens having the above-described configurationpreferably satisfies the following conditional expression (17):3<|f5|/f<60  (17)

According to a fifteenth aspect of the invention, when the fourth lenshas the focal length f4 and the sixth lens has a focal length f6, theimaging lens having the above-described configuration preferablysatisfies the following conditional expression (18):−1.3<f4/f6<−0.6  (18)

When the imaging lens satisfies the conditional expression (18), it isachievable to satisfactorily restrain the chromatic aberration and theastigmatism within satisfactory range, while downsizing of the imaginglens. When the value exceeds the upper limit of −0.6, it is advantageousfor downsizing of the imaging lens. However, it is difficult to securethe back focal length. Moreover, in the astigmatism, the sagittal imagesurface tilts to the object side and the astigmatic differenceincreases. Therefore, it is difficult to obtain satisfactoryimage-forming performance. On the other hand, when the value is belowthe lower limit of −1.3, the axial chromatic aberration and thechromatic aberration of magnification are both insufficiently corrected.In addition, in the astigmatism, the sagittal image surface tilts to theimage plane side and the astigmatic difference increases. In addition,the field curvature is excessively corrected. Therefore, it is difficultto obtain satisfactory image-forming performance.

According to a sixteenth aspect of the invention, when the second lensgroup has the focal length F2 and the sixth lens has a focal length f6,the imaging lens of the invention preferably satisfies the followingconditional expression (19):−1.5<f6/F2<−0.1  (19)

When the imaging lens satisfies the conditional expression (19), it ispossible to restrain the chromatic aberration, the field curvature, andthe distortion within satisfactory ranges in a balanced manner. When thevalue exceeds the upper limit of −0.1, the axial chromatic aberrationand the chromatic aberration of magnification are both excessivelycorrected. Moreover, in the astigmatism, the sagittal image surfacetilts to the image plane side, and the astigmatic difference increases.The field curvature is excessively corrected. In addition, thedistortion increases in a positive direction. Therefore, it is difficultto obtain satisfactory image-forming performance. On the other hand,when the value is below the lower limit of −1.5, it is advantageous forcorrection of the chromatic aberration. However, in the astigmatism, thesagittal image surface tilts to the object side and the astigmaticdifference increases. Therefore, it is difficult to obtain satisfactoryimage-forming performance.

When the imaging lens of the invention has an angle of view 2ω, theimaging lens preferably satisfies 70°≤2ω. When the imaging lenssatisfies the conditional expression, the imaging lens can have a widerangle of view, and it is suitably achievable to attain both downsizingof the imaging lens and wider angle of view of the imaging lens.

According to the present invention, as described above, the shapes ofthe lenses are specified using positive/negative signs of the curvatureradii thereof. Whether the curvature radius of the lens is positive ornegative is determined based on general definition. More specifically,taking a traveling direction of light as positive, if a center of acurvature radius is on the image plane side when viewed from a lenssurface, the curvature radius is positive. If a center of a curvatureradius is on the object side, the curvature radius is negative.Therefore, “an object side surface, a curvature radius of which ispositive” means the object side surface is a convex surface. “An objectside surface, a curvature radius of which is negative” means the objectside surface is a concave surface. “An image plane side surface, acurvature radius of which is positive” means the image plane sidesurface is a concave surface. “An image plane side surface, a curvatureradius of which is negative” means the image plane side surface is aconvex surface. Here, a curvature radius used herein refers to aparaxial curvature radius, and may not fit to general shapes of thelenses in their sectional views all the time.

According to the imaging lens of the present invention, it is possibleto provide a small-sized imaging lens that is especially suitable formounting in a small-sized camera, while having high resolution withsatisfactory correction of aberrations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view of a schematic configuration of an imaginglens in Numerical Data Example 1 according to an embodiment of thepresent invention;

FIG. 2 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 1;

FIG. 3 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 1;

FIG. 4 shows a sectional view of a schematic configuration of an imaginglens in Numerical Data Example 2 according to the embodiment of thepresent invention;

FIG. 5 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 4;

FIG. 6 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 4;

FIG. 7 shows a sectional view of a schematic configuration of an imaginglens in Numerical Data Example 3 according to the embodiment of thepresent invention;

FIG. 8 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 7;

FIG. 9 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 7;

FIG. 10 shows a sectional view of a schematic configuration of animaging lens in Numerical Data Example 4 according to the embodiment ofthe present invention;

FIG. 11 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 10;

FIG. 12 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 10;

FIG. 13 shows a sectional view of a schematic configuration of animaging lens in Numerical Data Example 5 according to the embodiment ofthe present invention;

FIG. 14 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 13; and

FIG. 15 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 13.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereunder, referring to the accompanying drawings, an embodiment of thepresent invention will be fully described.

FIGS. 1, 4, 7, 10, and 13 are schematic sectional views of the imaginglenses in Numerical Data Examples 1 to 5 according to the embodiment,respectively. Since the imaging lenses in those Numerical Data Exampleshave the same basic configuration, the lens configuration of theembodiment will be described with reference to the illustrativesectional view of Numerical Data Example 1.

As shown in FIG. 1, according to the embodiment, the imaging lensincludes a first lens group G1 having positive refractive power, and asecond lens group G2 having negative refractive power, arranged in theorder from an object side to an image plane side. The second lens groupG2 includes a front side lens group Gf having negative refractive powerand a rear side lens group Gr having positive refractive power. Betweenthe second lens group G2 and an image plane IM of an imaging element,there is provided a filter 10. The filter 10 is omissible.

The first lens group G1 includes a first lens L1 having positiverefractive power, an aperture stop ST, a second lens L2 having negativerefractive power, and a third lens L3 having positive refractive power,arranged in the order from an object side. According to the embodiment,in the imaging lens, there is provided the aperture stop ST on an imageplane-side surface of the first lens L1. The position of the aperturestop ST is not limited to between the first lens L1 and the second lensL2 as in the imaging lens of Numerical Data Example 1. For example, theaperture stop ST may be disposed on the object side of the first lensL1. Accordingly, in case of a so-called “front aperture-type” lensconfiguration, in which the aperture stop ST is disposed on the objectside of the imaging lens, it is achievable to improve assemblingefficiency and to reduce the manufacturing cost of the imaging lens.

On the other hand, in case of a so-called “mid aperture-type” lensconfiguration, in which the aperture stop ST is disposed between thefirst lens L1 and the second lens L2 as in Numerical Data Example 1, aneffective diameter of the first lens L1 is large in comparison with thetotal optical length of the imaging lens. As a result, the presence ofthe imaging lens in a camera is emphasized. Therefore, it is possible toappeal to users by the luxurious impression, high lens performance, etc.as a part of design of the camera.

In the first lens group G1, the first lens L1 is formed in a shape suchthat a curvature radius r1 of an object-side surface thereof is positiveand a curvature radius r2 of an image plane-side surface thereof isnegative, so as to have a shape of a biconvex lens near the optical axisX. The shape of the first lens L1 is not limited to the one in NumericalData Example 1. The first lens L1 can be formed in any shape as long asthe curvature radius r1 of the object-side surface thereof is positive.Therefore, the first lens L1 may be also formed in a shape, such thatthe curvature radius r2 is positive, so as to have a shape of a meniscuslens directing a convex surface thereof on the object side near anoptical axis X.

The second lens L2 is formed in a shape such that a curvature radius r3of an object-side surface thereof is negative and a curvature radius r4of an image plane-side surface thereof is positive, so as to have ashape of a biconcave lens near the optical axis X. The shape of thesecond lens L2 is not limited to the one in Numerical Data Example 1.The second lens can be formed in any shape, as long as the curvatureradius r3 of the object-side surface thereof is negative. Numerical DataExamples 2 through 4 are examples, in which the second lens L2 is formedin a shape, such that the curvature radius r4 is negative, i.e., so asto have a shape of a meniscus lens directing a concave surface thereofto the object side near the optical axis X.

The third lens L3 is formed in a shape such that a curvature radius r5of an object-side surface thereof and a curvature radius r6 of an imageplane-side surface thereof are both positive, so as to have a shape of ameniscus lens directing a convex surface thereof to the object side nearthe optical axis X. The shape of the third lens L3 is not limited to theone in Numerical Data Example 1. The third lens can be formed in anyshape, as long as the curvature radius r5 of the object-side surface ispositive. Numerical Data Examples 2 through 5 are examples, in which thethird lens L3 is formed in a shape, such that the curvature radius r6 isnegative, i.e., so as to have a shape of a biconvex lens near theoptical axis X.

The second lens group G2 includes a fourth lens L4 having negativerefractive power, a fifth lens L5 having positive refractive power, asixth lens L6 having positive refractive power, and a seventh lens L7having negative refractive power. In the second lens group G2, the fifthlens has the weakest refractive power. The second lens group G2 can beconfigured in any manner as long as the composite refractive power ofthose four lenses is negative. Numerical Data Examples 1 through 4 areexamples of a lens configuration, in which the fifth lens L5 haspositive refractive power in the second lens group G2. Numerical DataExample 5 is an example of a lens configuration, in which the fifth lensL5 has negative refractive power in the second lens group G2.

In the second lens group G2, the fourth lens L4 is formed in a shapesuch that a curvature radius r7 (=R4f) of an object-side surface thereofand a curvature radius r8 (=R4r) of an image plane-side surface thereofare both negative, so as to have a shape of a meniscus lens directing aconcave surface thereof to the object side near the optical axis X. Theshape of the fourth lens L4 is not limited to the one in Numerical DataExample 1. The fourth lens L4 can be formed in any shape, as long as thecurvature radius r7 of the object-side surface is negative.

The fifth lens L5 is formed in a shape such that a curvature radius r9of an object-side surface thereof and a curvature radius r10 of an imageplane-side surface thereof are both positive, so as to have a shape of ameniscus lens directing a convex surface thereof to the object side nearthe optical axis X.

The sixth lens L6 is formed in a shape such that a curvature radius r11of an object-side surface thereof and a curvature radius r12 of an imageplane-side surface thereof are both positive, so as to have a shape of ameniscus lens directing a convex surface thereof to the object side nearthe optical axis X. The shape of the sixth lens L6 is not limited to theone in Numerical Data Example 1. The sixth lens L6 can be formed in anyshape, as long as the curvature radius r11 of the object-side surface ispositive. Numerical Data Example 4 is an example, in which the sixthlens L6 is formed in a shape, such that the curvature radius r12 isnegative, i.e., so as to have a shape of a biconvex lens near theoptical axis X.

The seventh lens L7 is formed in a shape such that a curvature radiusr13 of an object-side surface thereof and a curvature radius r14 (=R7r)of an image plane-side surface thereof are both positive, so as to havea shape of a meniscus lens directing a convex surface thereof to theobject side near the optical axis X. The shape of the seventh lens L7 isnot limited to the one in Numerical Data Example 1. The seventh lens L7can be formed in any shape, as long as the curvature radius r14 ispositive. Numerical Data Example 4 is an example, in which the seventhlens L7 is formed in a shape, such that the curvature radius r13 isnegative, i.e., so as to have a shape of a biconcave lens near theoptical axis X.

In addition, in the fifth lens L5 through the seventh lens L7, both theobject-side surfaces and the image plane-side surfaces thereof, or oneof the object-side surfaces and the image plane-side surfaces are formedas aspheric shapes having inflexion points. In the imaging lens ofNumerical Data Example 1, the fifth lens L5, the sixth lens L6, and theseventh lens L7 are formed as aspheric shapes having an inflexion pointon the both surfaces of each of the fifth lens L5 through the seventhlens L7. With those shapes of the fifth lens L5 through the seventh lensL7, it is achievable to satisfactorily correct the off-axis chromaticaberration of magnification as well as the axial chromatic aberration.In addition, it is also achievable to suitably restrain an incidentangle of a light beam emitted from the imaging lens to the image planeIM within the range of CRA. Here, depending on required opticalperformance or a required level of downsizing of the imaging lens, it ispossible to form both the fifth lens L5 and the sixth lens L6 or one ofthe fifth lens L5 and the sixth lens L6 as aspheric shape(s) not havingan inflexion point on the both surfaces thereof.

According to the embodiment, the imaging lens satisfies the followingconditional expressions (1) to (19):1.2<La/f<1.8  (1)1.3<La/Hmax<1.8  (2)0.05<Da/f<0.3  (3)35<νd1<75  (4)15<νd2<35  (5)35<νd3<75  (6)−0.6<R4f/f<−0.1  (7)−1.2<R4r/f<−0.3  (8)0.2<R7r/f<0.6  (9)15<νd4<35  (10)0.6<F1/f<1.3  (11)−8<f2/F1<−1.5  (12)−1.5<Ff/Fr<−0.1  (13)0.02<Db/f<0.1  (14)1<Fr/f<10  (15)−3<f4/f<−1  (16)3<|f5|/f<60  (17)−1.3<f4/f6<−0.6  (18)−1.5<f6/F2<−0.1  (19)

In the above conditional expressions,

f: Focal length of the whole lens system

f2: Focal length of a second lens L2

f4: Focal length of a fourth lens L4

f5: Focal length of a fifth lens L5

f6: Focal length of a sixth lens L6

F1: Focal length of a first lens group G1

F2: Focal length of a second lens group G2

Ff: Focal length of a front side lens group Gf

Fr: Focal length of a rear side lens group Gr

La: Distance on the optical axis X from an object-side surface of thefirst lens L1 to an image plane IM (length in air for a filter 10)

Da: Distance on the optical axis X between the first lens group G1 andthe second lens group G2

Db: Distance on the optical axis X between the front side lens group Gfand the rear side lens group Gr

νd1: Abbe's number of the first lens L1

νd2: Abbe's number of the second lens L2

νd3: Abbe's number of the third lens L3

νd4: Abbe's number of the fourth lens L4

R4f: Curvature radius of an object-side surface of the fourth lens L4

R4r: Curvature radius of an image plane-side surface of the fourth lensL4

R7r: Curvature radius of an image plane-side surface of the seventh lensL7

Here, it is not necessary to satisfy all of the conditional expressions,and it is achievable to obtain an effect corresponding to the respectiveconditional expression when any single one of the conditionalexpressions is individually satisfied.

In the embodiment, all lens surfaces are formed as an aspheric surface.The aspheric shapes of the lens surfaces are expressed as follows:

$Z = {\frac{C \cdot H^{2}}{1 + \sqrt{1 - {\left( {1 + k} \right) \cdot C^{2} \cdot H^{2}}}} + {\sum\left( {{An} \cdot H^{n}} \right)}}$

In the above formula,

Z: Distance on an optical axis

H: Distance from the optical axis in a direction perpendicular to theoptical axis

C: Paraxial curvature (=1/r, r: paraxial curvature radius)

k: conic constant

An: n-order aspheric constant

Next, Numerical Data Examples of the imaging lens of the embodiment willbe described. In each Numerical Data Example, f represents a focallength of the whole lens system, Fno represents an F-number, and corepresents a half angle of view, respectively. In addition, i representsa surface number counted from the object side, r represents a curvatureradius, d represents a distance on the optical axis between lenssurfaces (surface spacing), nd represents a refractive index, and νdrepresents an Abbe's number, respectively. Here, aspheric surfaces areindicated with surface numbers i affixed with * (asterisk).

Numerical Data Example 1

Basic Lens Data

TABLE 1 f = 6.37 mm Fno = 2.1 ω = 36.5° i r d nd νd [mm] ∞ ∞ L1  1*3.938 0.664 1.5346 56.1 f1 = 6.732  2* (ST) −39.287 0.043 L2  3* −20.3920.249 1.6355 23.9 f2 = −18.353  4* 27.375 0.030 L3  5* 12.783 0.4541.5346 56.1 f3 = 27.920  6* 87.942 1.321 (=Da) L4  7* −2.706 0.2901.6355 23.9 f4 = −12.700  8* −4.241 0.039 L5  9* 5.324 0.804 1.5346 56.1f5 = 23.008 10* 8.893 0.458 (=Db) L6 11* 3.023 0.870 1.5346 56.1 f6 =10.154 12* 6.139 0.948 L7 13* 3.899 0.846 1.5346 56.1 f7 = −8.371 14*1.926 0.500 15 ∞ 0.210 1.5168 64.2 16 ∞ 0.560 (IM) ∞Hmax=4.71La=8.214F1=7.631F2=−31.267Ff=−27.920Fr=58.077Aspheric Surface Data

TABLE 2 i k A4 A6 A8 A10 A12 A14 A16 1 0 −9.524E−03 −3.649E−03−1.721E−04 5.316E−05 −1.331E−05 −5.864E−06 1.745E−06 2 0 1.733E−02−4.592E−02 2.795E−02 −8.522E−03 1.216E−03 −6.720E−05 3.155E−06 3 05.529E−02 −6.343E−02 3.238E−02 −8.938E−03 1.114E−03 8.147E−06 −9.325E−064 0 5.100E−02 −4.564E−02 1.684E−02 −3.284E−03 3.997E−05 1.961E−04−3.990E−05 5 0 1.637E−02 −1.257E−02 7.554E−03 −9.676E−04 −1.287E−05−2.479E−05 5.859E−06 6 0 −8.571E−03 2.437E−03 3.153E−03 −9.565E−045.912E−06 1.579E−05 −1.306E−06 7 0 −1.729E−02 4.024E−03 2.953E−03−8.843E−04 −7.623E−05 1.622E−05 4.166E−08 8 0 −2.763E−02 8.731E−03−4.653E−04 3.822E−04 −1.862E−04 7.797E−06 3.073E−06 9 0 −1.238E−025.084E−04 −2.256E−05 −3.302E−06 −9.424E−06 1.855E−06 −3.141E−07 10 0−1.407E−02 −1.314E−03 1.460E−04 1.880E−07 4.684E−07 −6.436E−07−1.461E−08 11 0 −1.483E−02 −1.411E−03 −6.919E−06 −1.842E−05 4.691E−073.865E−07 −3.283E−08 12 0 7.722E−03 −3.831E−03 3.406E−04 −7.814E−06−2.073E−07 −1.517E−08 1.388E−09 13 0 −6.169E−02 5.589E−03 −1.484E−04−2.147E−06 −8.704E−08 1.393E−08 −4.180E−10 14 −3.763 −2.616E−023.300E−03 −2.298E−04 6.135E−06 1.552E−07 −1.233E−08 2.098E−10

The values of the respective conditional expressions are as follows:La/f=1.29La/Hmax=1.74Da/f=0.21R4f/f=−0.42R4r/f=−0.67R7r/f=0.30F1/f=1.20f2/F1=−2.41Ff/Fr=−0.48Db/f=0.07Fr/f=9.12f4/f=−1.99|f5|/f=3.61f4/f6=−1.25f6/F2=−0.32

Accordingly, the imaging lens of Numerical Data Example 1 satisfies theabove-described conditional expressions.

FIG. 2 shows a lateral aberration that corresponds to a ratio H of eachimage height to the maximum image height Hmax (hereinafter referred toas “image height ratio H”), which is divided into a tangential directionand a sagittal direction (The same is true for FIGS. 5, 8, 11, and 14).Furthermore, FIG. 3 shows a spherical aberration (mm), astigmatism (mm),and a distortion (%), respectively. In the astigmatism diagram, anaberration on a sagittal image surface S and an aberration on atangential image surface T are respectively indicated (The same is truefor FIGS. 6, 9, 12, and 15). As shown in FIGS. 2 and 3, according to theimaging lens of Numerical Data Example 1, the aberrations aresatisfactorily corrected.

Numerical Data Example 2

Basic Lens Data

TABLE 3 f = 5.86 mm Fno = 2.1 ω = 38.8° i r d nd νd [mm] ∞ ∞ L1  1*4.247 0.530 1.5346 56.1 f1 = 6.562  2* (ST) −19.282 0.082 L2  3* −12.3360.250 1.6355 23.9 f2 = −29.787  4* −35.693 0.030 L3  5* 21.621 0.5931.5346 56.1 f3 = 17.006  6* −15.538 1.104 (=Da) L4  7* −2.332 0.5021.6355 23.9 f4 = −7.972  8* −4.683 0.040 L5  9* 8.514 0.651 1.5346 56.1f5 = 243.113 10* 8.868 0.283 (=Db) L6 11* 3.047 1.022 1.5346 56.1 f6 =6.676 12* 18.389 0.630 L7 13* 3.882 1.047 1.5346 56.1 f7 = −9.130 14*1.959 0.550 15 ∞ 0.210 1.5168 64.2 16 ∞ 0.527 (IM) ∞Hmax=4.71La=7.979F1=5.779F2=−15.842Ff=−8.053Fr=10.953Aspheric Surface Data

TABLE 4 i k A4 A6 A8 A10 A12 A14 A16 1 0 −1.264E−02 −5.082E−03−6.651E−04 1.405E−04 −3.972E−05 −1.534E−05 1.483E−05 2 0 1.818E−02−4.778E−02 2.785E−02 −8.590E−03 1.170E−03 4.453E−05 −1.634E−05 3 05.092E−02 −6.629E−02 3.599E−02 −1.131E−02 1.933E−03 −2.911E−05−3.224E−05 4 0 4.735E−02 −4.459E−02 1.663E−02 −3.167E−03 1.456E−051.926E−04 −4.147E−05 5 0 2.314E−02 −1.340E−02 6.956E−03 −1.123E−037.064E−05 −2.643E−05 3.924E−06 6 0 −1.327E−02 2.457E−03 1.706E−03−7.143E−04 6.572E−05 1.442E−06 4.841E−09 7 0 −1.401E−02 6.281E−033.671E−03 −9.785E−04 −1.194E−04 2.181E−05 6.022E−06 8 0 −2.634E−029.741E−03 −4.836E−04 3.794E−04 −1.563E−04 8.296E−06 1.995E−06 9 0−1.307E−02 −5.845E−05 −5.725E−05 1.391E−06 −8.526E−06 1.623E−06−3.398E−07 10 0 −2.203E−02 −1.065E−03 1.218E−04 −3.888E−06 6.221E−07−6.052E−07 1.624E−08 11 0 −1.995E−02 −9.270E−04 −4.110E−05 −1.979E−058.362E−07 4.005E−07 −3.072E−08 12 0 8.237E−03 −4.140E−03 3.346E−04−6.210E−06 −2.274E−07 −3.262E−09 1.169E−09 13 0 −6.342E−02 5.772E−03−1.509E−04 −2.142E−06 −8.095E−08 −4.799E−09 7.192E−10 14 −3.745−2.391E−02 2.985E−03 −1.995E−04 4.986E−06 1.627E−07 −1.316E−08 2.278E−10

The values of the respective conditional expressions are as follows:La/f=1.36La/Hmax=1.69Da/f=0.19R4f/f=−0.40R4r/f=−0.80R7r/f=0.33F1/f=0.99f2/F1=−5.15Ff/Fr=−0.74Db/f=0.05Fr/f=1.87f4/f=−1.36|f5|/f=41.49f4/f6=−1.19f6/F2=−0.42

Accordingly, the imaging lens of Numerical Data Example 2 satisfies theabove-described conditional expressions.

FIG. 5 shows a lateral aberration that corresponds to the image heightratio H, and FIG. 6 shows a spherical aberration (mm), astigmatism (mm),and a distortion (%), respectively. As shown in FIGS. 5 and 6, accordingto the imaging lens of Numerical Data Example 2, the aberrations arealso satisfactorily corrected.

Numerical Data Example 3

Basic Lens Data

TABLE 5 f = 5.79 mm Fno = 2.2 ω = 39.1° i r d nd νd [mm] ∞ ∞ L1  1*5.165 0.393 1.5346 56.1 f1 = 7.067  2* (ST) −13.697 0.064 L2  3* −12.3180.250 1.6355 23.9 f2 = −29.059  4* −37.287 0.027 L3  5* 20.086 0.5761.5346 56.1 f3 = 31.583  6* −104.860 0.930 (=Da) L4  7* −2.544 0.3371.6355 23.9 f4 = −7.823  8* −5.479 0.040 L5  9* 4.743 0.773 1.5346 56.1f5 = 34.776 10* 6.006 0.178 (=Db) L6 11* 2.656 1.180 1.5346 56.1 f6 =6.236 12* 11.041 0.842 L7 13* 3.699 1.231 1.5346 56.1 f7 = −9.377 14*1.881 0.600 15 ∞ 0.210 1.5168 64.2 16 ∞ 0.507 (IM) ∞Hmax=4.71La=8.066F1=7.260F2=−53.458Ff=−9.692Fr=8.253Aspheric Surface Data

TABLE 6 i k A4 A6 A8 A10 A12 A14 A16 1 0 −1.094E−02 −4.386E−03−5.344E−04 1.609E−04 −3.619E−05 −1.860E−05 9.232E−06 2 0 2.101E−02−4.684E−02 2.797E−02 −8.624E−03 1.140E−03 3.033E−05 −1.788E−05 3 05.345E−02 −6.616E−02 3.609E−02 −1.125E−02 1.945E−03 −3.350E−05−3.693E−05 4 0 5.127E−02 −4.407E−02 1.677E−02 −3.111E−03 3.625E−051.950E−04 −4.313E−05 5 0 1.904E−02 −1.314E−02 7.050E−03 −1.111E−037.178E−05 −2.641E−05 4.362E−06 6 0 −2.231E−02 2.784E−03 1.788E−03−6.986E−04 7.193E−05 2.267E−06 −4.848E−07 7 0 −1.632E−02 4.605E−033.685E−03 −9.116E−04 −1.098E−04 1.800E−05 4.218E−06 8 0 −3.033E−028.741E−03 −6.101E−04 3.569E−04 −1.586E−04 8.677E−06 2.027E−06 9 0−1.129E−02 7.423E−04 −2.441E−05 −3.801E−06 −9.774E−06 1.742E−06−1.832E−07 10 0 −2.230E−02 −3.067E−04 1.750E−04 −1.477E−05 −1.374E−06−5.129E−07 5.729E−08 11 0 −2.974E−02 −1.253E−04 −1.675E−04 −3.670E−054.570E−08 4.003E−07 −3.680E−08 12 0 9.254E−03 −3.571E−03 3.443E−04−6.766E−06 −3.424E−07 −1.826E−08 2.515E−09 13 0 −6.145E−02 5.587E−03−1.488E−04 −1.563E−06 −3.590E−08 −5.686E−09 4.612E−10 14 −3.649−2.336E−02 2.890E−03 −2.031E−04 5.199E−06 1.752E−07 −1.298E−08 2.020E−10

The values of the respective conditional expressions are as follows:La/f=1.39La/Hmax=1.71Da/f=0.16R4f/f=−0.44R4r/f=−0.95R7r/f=0.32F1/f=1.25f2/F1=−4.00Ff/Fr=−1.17Db/f=0.03Fr/f=1.43f4/f=−1.35|f5|/f=6.01f4/f6=−1.25f6/F2=−0.12

Accordingly, the imaging lens of Numerical Data Example 3 satisfies theabove-described conditional expressions.

FIG. 8 shows a lateral aberration that corresponds to the image heightratio H, and FIG. 9 shows a spherical aberration (mm), astigmatism (mm),and a distortion (%), respectively. As shown in FIGS. 8 and 9, accordingto the imaging lens of Numerical Data Example 3, the aberrations arealso satisfactorily corrected.

Numerical Data Example 4

Basic Lens Data

TABLE 7 f = 6.37 mm Fno = 2.1 ω = 36.5° i r d nd νd [mm] ∞ ∞ L1  1*3.767 0.626 1.5346 56.1 f1 = 6.613  2* (ST) −54.068 0.080 L2  3* −11.5790.254 1.6355 23.9 f2 = −27.758  4* −33.982 0.030 L3  5* 13.110 0.5781.5346 56.1 f3 = 17.789  6* −34.097 1.080 (=Da) L4  7* −2.595 0.5311.6355 23.9 f4 = −8.588  8* −5.340 0.071 L5  9* 8.461 0.670 1.5346 56.1f5 = 26.534 10* 20.390 0.396 (=Db) L6 11* 3.908 0.726 1.5346 56.1 f6 =6.842 12* −53.272 0.892 L7 13* −100.605 0.960 1.5346 56.1 f7 = −5.55614* 3.071 0.450 15 ∞ 0.210 1.5168 64.2 16 ∞ 0.616 (IM) ∞Hmax=4.71La=8.098F1=5.960F2=−11.913Ff=−13.024Fr=58.076Aspheric Surface Data

TABLE 8 i k A4 A6 A8 A10 A12 A14 A16 1 0 −9.250E−03 −4.217E−03−1.604E−04 1.137E−04 −9.526E−05 −2.606E−05 1.481E−05 2 0 1.200E−02−4.517E−02 2.779E−02 −8.608E−03 1.105E−03 3.494E−05 −1.162E−05 3 05.142E−02 −6.318E−02 3.517E−02 −1.130E−02 1.884E−03 −2.973E−05−2.281E−05 4 0 5.179E−02 −4.356E−02 1.625E−02 −3.173E−03 3.828E−061.945E−04 −3.704E−05 5 0 1.451E−02 −1.389E−02 7.260E−03 −1.099E−031.207E−04 −3.821E−05 4.104E−06 6 0 −1.623E−02 3.820E−03 1.098E−03−4.868E−04 5.218E−05 −1.199E−06 3.269E−09 7 0 −1.079E−02 4.811E−032.115E−03 −3.571E−04 −1.688E−04 9.883E−06 6.453E−06 8 0 −2.524E−029.124E−03 −5.580E−04 2.475E−04 −1.174E−04 9.584E−06 1.122E−06 9 0−1.863E−02 1.062E−05 −2.786E−04 −4.143E−06 −1.028E−05 1.506E−06−6.955E−07 10 0 −1.545E−02 −3.165E−03 1.732E−04 1.233E−05 −1.601E−06−1.334E−06 −3.675E−09 11 0 −1.712E−02 7.142E−05 −2.383E−04 −2.020E−054.869E−06 2.348E−07 −5.874E−08 12 0 5.335E−03 −2.690E−03 1.764E−04−1.881E−06 −8.073E−08 −4.802E−09 1.438E−09 13 0 −4.503E−02 4.602E−03−4.544E−05 −5.327E−06 −3.290E−07 −5.447E−09 1.870E−09 14 −6.853−1.842E−02 2.240E−03 −1.570E−04 4.092E−06 1.001E−07 −7.956E−09 1.096E−10

The values of the respective conditional expressions are as follows:La/f=1.27La/Hmax=1.72Da/f=0.17R4f/f=−0.41R4r/f=−0.84R7r/f=0.48F1/f=0.94f2/F1=−4.66Ff/Fr=−0.22Db/f=0.06Fr/f=9.12f4/f=−1.35|f5|/f=4.17f4/f6=−1.26f6/F2=−0.57

Accordingly, the imaging lens of Numerical Data Example 4 satisfies theabove-described conditional expressions.

FIG. 11 shows a lateral aberration that corresponds to the image heightratio H, and FIG. 12 shows a spherical aberration (mm), astigmatism(mm), and a distortion (%), respectively. As shown in FIGS. 11 and 12,according to the imaging lens of Numerical Data Example 4, theaberrations are also satisfactorily corrected.

Numerical Data Example 5

Basic Lens Data

TABLE 9 f = 6.00 mm Fno = 2.1 ω = 38.1° i r d nd νd [mm] ∞ ∞ L1  1*3.722 0.535 1.5346 56.1 f1 = 6.475  2* (ST) −46.957 0.079 L2  3* −20.7680.275 1.6355 23.9 f2 = −20.445  4* 34.881 0.024 L3  5* 14.193 0.6481.5346 56.1 f3 = 14.324  6* −16.365 1.110 (=Da) L4  7* −2.414 0.3901.6355 23.9 f4 = −13.925  8* −3.528 0.063 L5  9* 4.793 0.547 1.5346 56.1f5 = −269.532 10* 4.454 0.426 (=Db) L6 11* 4.019 0.940 1.5346 56.1 f6 =11.100 12* 11.443 0.436 L7 13* 3.724 1.018 1.5346 56.1 f7 = −10.009 14*1.987 0.520 15 ∞ 0.210 1.5168 64.2 16 ∞ 0.548 (IM) ∞Hmax=4.71La=7.697F1=5.836F2=−11.895Ff=−12.683Fr=54.582Aspheric Surface Data

TABLE 10 i k A4 A6 A8 A10 A12 A14 A16 1 0 −1.359E−02 −4.469E−03−2.041E−03 8.120E−04 7.378E−05 −4.124E−05 −2.307E−07 2 0 1.080E−02−4.660E−02 2.929E−02 −8.414E−03 9.440E−04 2.773E−05 −1.172E−05 3 04.918E−02 −6.650E−02 3.681E−02 −1.103E−02 1.621E−03 −1.727E−04 1.995E−054 0 5.289E−02 −4.723E−02 1.660E−02 −3.536E−03 2.018E−04 9.148E−05−1.815E−05 5 0 2.289E−02 −1.315E−02 6.875E−03 −1.143E−03 9.490E−05−2.895E−05 4.463E−06 6 0 −1.380E−02 1.696E−03 2.492E−03 −8.062E−041.068E−04 −2.532E−05 3.318E−06 7 0 −1.762E−02 6.260E−03 3.340E−03−1.034E−03 −5.898E−05 1.966E−05 2.645E−06 8 0 −2.423E−02 9.781E−03−3.939E−04 3.744E−04 −1.535E−04 8.418E−06 2.799E−06 9 0 −1.671E−026.725E−04 7.323E−06 2.023E−06 −7.353E−06 1.664E−06 −2.502E−07 10 0−1.851E−02 −3.809E−04 8.922E−05 8.701E−06 1.083E−06 −5.314E−07−2.072E−09 11 0 −1.331E−02 −2.209E−03 1.086E−05 −2.004E−05 8.310E−074.565E−07 −2.316E−08 12 0 5.541E−05 −4.116E−03 3.528E−04 −5.490E−06−1.607E−07 7.459E−10 1.183E−09 13 0 −6.201E−02 5.794E−03 −1.649E−04−2.483E−06 −1.099E−07 −4.418E−09 9.328E−10 14 −3.861 −2.471E−023.206E−03 −2.100E−04 4.851E−06 1.736E−07 −1.323E−08 2.359E−10

The values of the respective conditional expressions are as follows:La/f=1.28La/Hmax=1.63Da/f=0.19R4f/f=−0.40R4r/f=−0.59R7r/f=0.33F1/f=0.97f2/F1=−3.50Ff/Fr=−0.23Db/f=0.07Fr/f=9.10f4/f=−2.32|f5|/f=44.92f4/f6=−1.25f6/F2=−0.93

Accordingly, the imaging lens of Numerical Data Example 5 satisfies theabove-described conditional expressions.

FIG. 14 shows a lateral aberration that corresponds to the image heightratio H, and FIG. 15 shows a spherical aberration (mm), astigmatism(mm), and a distortion (%), respectively. As shown in FIGS. 14 and 15,according to the imaging lens of Numerical Data Example 5, theaberrations are also satisfactorily corrected.

According to the imaging lens of the embodiment described above, it isachievable to have a wide angle of view (2ω) of 70° or greater.According to Numerical Data Examples 1 to 5, the imaging lenses havewide angles of view of 73.0° to 78.2°. According to the imaging lens ofthe embodiment, it is possible to take an image over a wider range thanthat taken by a conventional imaging lens.

Moreover, in these years, with advancement in digital zoom technology,which enables to enlarge any area of an image obtained through animaging lens by image processing, an imaging element having a high pixelcount is often used in combination with a high-resolution imaging lens.In case of such an imaging element with a high pixel count, alight-receiving area of each pixel decreases, so that an image tends tobe dark. According to the imaging lenses of Numerical Data Examples 1 to5, the Fnos are as small as 2.1 to 2.2. According to the imaging lens ofthe embodiment, it is possible to obtain a sufficiently bright imageapplicable to a high pixel count imaging element.

Accordingly, when the imaging lens of the embodiment is mounted in animaging optical system, such as cameras built in portable devicesincluding cellular phones, portable information terminals, andsmartphones, digital still cameras, security cameras, onboard cameras,and network cameras, it is possible to attain both high performance anddownsizing of the cameras.

The present invention is applicable to an imaging lens to be mounted inrelatively small cameras, such as cameras to be built in portabledevices including cellular phones, smartphones, and portable informationterminals, digital still cameras, security cameras, onboard cameras, andnetwork cameras.

The disclosure of Japanese Patent Application No. 2015-171027, filed onAug. 31, 2015, is incorporated in the application by reference.

While the present invention has been explained with reference to thespecific embodiment of the present invention, the explanation isillustrative and the present invention is limited only by the appendedclaims.

What is claimed is:
 1. An imaging lens comprising: a first lens group;and a second lens group, arranged in this order from an object side toan image plane side, wherein said first lens group includes a firstlens, a second lens, and a third lens, arranged in this order from theobject side to the image plane side, said second lens group includes afront side lens group and a rear side lens group, arranged in this orderfrom the object side to the image plane side, said front side lens groupincludes a fourth lens and a fifth lens, said rear side lens groupincludes a sixth lens having two aspheric surfaces and a seventh lenshaving two aspheric surfaces, said imaging lens has a total of sevensingle lenses, said first lens, said second lens, said third lens, saidfourth lens, said fifth lens, said sixth lens, and said seventh lens arearranged respectively with a space in between, said third lens is formedin a shape so that a surface thereof on the object side and a surfacethereof on the image plane side are convex near an optical axis thereof,said fourth lens is formed in a shape so that a surface thereof on theobject side is concave near an optical axis thereof, said fifth lens isformed in a shape so that a surface thereof on the image plane side isconcave near an optical axis thereof, and said rear side lens group hasa focal length Fr so that the following conditional expression issatisfied:1<Fr/f<10, where f is a focal length of a whole lens system.
 2. Theimaging lens according to claim 1, wherein said fourth lens is formed inthe shape so that a surface thereof on the image plane side has acurvature radius R4r so that the following conditional expression issatisfied:−1.2<R4r/f<−0.3.
 3. The imaging lens according to claim 1, wherein saidseventh lens is formed in a shape so that a surface thereof on the imageplane side has a curvature radius R7r so that the following conditionalexpression is satisfied:0.2<R7r/f<0.6.
 4. The imaging lens according to claim 1, wherein saidfront side lens group has a focal length Ff so that the followingconditional expression is satisfied:−1.5<Ff/Fr<−0.1.
 5. The imaging lens according to claim 1, wherein saidfifth lens has a focal length f5 so that the following conditionalexpression is satisfied:3<|f5|/f<60.
 6. An imaging lens comprising: a first lens group; and asecond lens group, arranged in this order from an object side to animage plane side, wherein said first lens group includes a first lens, asecond lens, and a third lens, arranged in this order from the objectside to the image plane side, said second lens group includes a frontside lens group and a rear side lens group, arranged in this order fromthe object side to the image plane side, said front side lens groupincludes a fourth lens having negative refractive power and a fifthlens, said rear side lens group includes a sixth lens having twoaspheric surfaces and a seventh lens having two aspheric surfaces, saidimaging lens has a total of seven single lenses, said first lens, saidsecond lens, said third lens, said fourth lens, said fifth lens, saidsixth lens, and said seventh lens are arranged respectively with a spacein between, said third lens is formed in a shape so that a surfacethereof on the object side and a surface thereof on the image plane sideare convex near an optical axis thereof, said fourth lens is formed in ashape so that a surface thereof on the object side is concave near anoptical axis thereof, said fifth lens has at least one aspheric surface,and said fifth lens is formed in a shape so that a surface thereof onthe image plane side is concave near an optical axis thereof.
 7. Theimaging lens according to claim 6, wherein said fourth lens is formed inthe shape so that a surface thereof on the image plane side has acurvature radius R4r so that the following conditional expression issatisfied:−1.2<R4r/f<−0.3, where f is a focal length of a whole lens system. 8.The imaging lens according to claim 6, wherein said seventh lens isformed in a shape so that a surface thereof on the image plane side hasa curvature radius R7r so that the following conditional expression issatisfied:0.2<R7r/f<0.6, where f is a focal length of a whole lens system.
 9. Theimaging lens according to claim 6, wherein said front side lens grouphas a focal length Ff and said rear side lens group has a focal lengthFr so that the following conditional expression is satisfied:−1.5<Ff/Fr<−0.1.
 10. The imaging lens according to claim 6, wherein saidfifth lens has a focal length f5 so that the following conditionalexpression is satisfied:3<|f5|/f<60, where f is a focal length of a whole lens system.
 11. Animaging lens comprising: a first lens group; and a second lens group,arranged in this order from an object side to an image plane side,wherein said first lens group includes a first lens, a second lens, anda third lens, arranged in this order from the object side to the imageplane side, said second lens group includes a front side lens group anda rear side lens group, arranged in this order from the object side tothe image plane side, said front side lens group includes a fourth lensand a fifth lens, said rear side lens group includes a sixth lens havingtwo aspheric surfaces and a seventh lens having two aspheric surfaces,said imaging lens has a total of seven single lenses, said first lens,said second lens, said third lens, said fourth lens, said fifth lens,said sixth lens, and said seventh lens are arranged respectively with aspace in between, said third lens is formed in a shape so that a surfacethereof on the object side and a surface thereof on the image plane sideare convex near an optical axis thereof, said fourth lens is formed in ashape so that a surface thereof on the object side is concave near anoptical axis thereof, said fifth lens is formed in a shape so that asurface thereof on the image plane side is concave near an optical axisthereof, and said front side lens group has a focal length Ff and saidrear side lens group has a focal length Fr so that the followingconditional expression is satisfied:−1.5<Ff/Fr<−0.1.
 12. The imaging lens according to claim 11, whereinsaid fourth lens is formed in the shape so that a surface thereof on theimage plane side has a curvature radius R4r so that the followingconditional expression is satisfied:−1.2<R4r/f<−0.3, where f is a focal length of a whole lens system. 13.The imaging lens according to claim 11, wherein said seventh lens isformed in a shape so that a surface thereof on the image plane side hasa curvature radius R7r so that the following conditional expression issatisfied:0.2<R7r/f<0.6, where f is a focal length of a whole lens system.
 14. Theimaging lens according to claim 11, wherein said rear side lens grouphas the focal length Fr so that the following conditional expression issatisfied:1<Fr/f<10, where f is a focal length of a whole lens system.
 15. Theimaging lens according to claim 11, wherein said fifth lens has a focallength f5 so that the following conditional expression is satisfied:3<|f5|/f<60, where f is a focal length of a whole lens system.
 16. Animaging lens comprising: a first lens group; and a second lens group,arranged in this order from an object side to an image plane side,wherein said first lens group includes a first lens, a second lens, anda third lens, arranged in this order from the object side to the imageplane side, said second lens group includes a front side lens group anda rear side lens group, arranged in this order from the object side tothe image plane side, said front side lens group includes a fourth lensand a fifth lens, said rear side lens group includes a sixth lens havingtwo aspheric surfaces and a seventh lens having two aspheric surfaces,said imaging lens has a total of seven single lenses, said first lens,said second lens, said third lens, said fourth lens, said fifth lens,said sixth lens, and said seventh lens are arranged respectively with aspace in between, said third lens is formed in a shape so that a surfacethereof on the object side and a surface thereof on the image plane sideare convex near an optical axis thereof, said fourth lens is formed in ashape so that a surface thereof on the object side is concave near anoptical axis thereof, said fifth lens is formed in a shape so that asurface thereof on the image plane side is concave near an optical axisthereof, and said fifth lens has a focal length f5 so that the followingconditional expression is satisfied:3<|f5|/f<60, where f is a focal length of a whole lens system.
 17. Theimaging lens according to claim 16, wherein said fourth lens is formedin the shape so that a surface thereof on the image plane side has acurvature radius R4r so that the following conditional expression issatisfied:−1.2<R4r/f<−0.3.
 18. The imaging lens according to claim 16, whereinsaid seventh lens is formed in a shape so that a surface thereof on theimage plane side has a curvature radius R7r so that the followingconditional expression is satisfied:0.2<R7r/f<0.6.
 19. The imaging lens according to claim 16, wherein saidrear side lens group has a focal length Fr so that the followingconditional expression is satisfied:1<Fr/f<10.
 20. The imaging lens according to claim 16, wherein saidfront side lens group has a focal length Ff and said rear side lensgroup has a focal length Fr so that the following conditional expressionis satisfied:−1.5<Ff/Fr<−0.1.